Self-steering bogies

ABSTRACT

The invention concerns an inter-axle shear stiffening apparatus for a self-steering rail bogie and a self-steering rail bogie equipped with such apparatus. The apparatus has axle structures including axles ( 16, 16.1 ) which are journalled in axle box bearings ( 20, 20.1 ). Radial arms ( 30, 30.1 ) are connected rigidly to respective axle structures of the bogie an extend towards one another in a fore and aft direction. A lateral force transmitting device ( 60 ) acts between the arms to transmit lateral forces between them while accommodating relative lateral movement between them. The design of this device is such that, irrespective of the extent of relative movement between the arms, the device can only transmit between them lateral forces of limited, predetermined magnitude. This value is chosen such that the bogie is provided with sufficient inter-axle shear stiffness to enhance its hunting stability without excessive force couples being applied to the axle box bearings.

BACKGROUND TO THE INVENTION

THIS invention relates to self-steering bogies for rail vehicles and inparticular to the provision of inter-axle shear stiffness inself-steering bogies.

Inter-axle shear stiffness for self-steering bogies is commonly providedby means of cross-anchors which are fitted to the wheelset sub-frames,as proposed for instance in the known Scheffel cross-anchor design, orby means of A-frames which are connected to one another, at theirapices, on the transverse centre line of the bogie, as proposed forinstance in the known List Steering Arm design. However, on irregulartrack, and particularly at points and crossings, high shock loads areexerted on the wheelsets and transmitted to the sub-frames or A-frames.The frames must therefore be robust. Robustness is also necessary toensure that the forces transmitted to the frames do not generate undulyhigh force couples on the journal roller bearings of the bogie wheelsetswhich could shorten the service life of those bearings. The requiredrobustness results in heavy sub-frames or A-frames which considerablyincrease the unsprung wheelset mass and this can in turn reduce thehunting stability of the bogie at high speeds.

It is however understood that the inter-axle shear forces which arerequired to ensure effective wheelset guidance for hunting stability andcurving performance are only a fraction, typically no more than 30%, ofthe shock forces encountered at points and crossings.

Against this background the present invention proposes to provide anapparatus which will limit the transmission of shear forces between thewheelsets to a level at which adequate hunting stability and curvingperformance can be attained but which will nevertheless be acceptable tothe wheel journal roller bearings.

SUMMARY OF THE INVENTION

According to one aspect of the invention there is provided an inter-axleshear stiffening apparatus for a self-steering rail bogie having axlestructures including axles which are journalled in axle box bearings,the apparatus comprising arms which are rigidly connected or connectableto respective axle structures of the bogie to extend towards one anotherfrom the axle structures in generally fore and aft directions, andlateral force transmitting means for acting between the arms to transmitlateral forces between them while accommodating relative lateralmovement between the arms, wherein, irrespective of the extent ofrelative movement between the arms, the lateral force transmitting meansis only capable of transmitting between them lateral forces of limited,predetermined magnitude which provide the bogie with inter-axle shearstiffness to enhance hunting stability of the bogie but are insufficientto impose excessive force couples on the axle box bearings.

According to another aspect of the invention there is provided aself-steering rail bogie having axle structures including axlesjournalled in axle box bearings and including an inter-axle shearstiffening apparatus as summarised above, with the arms of the apparatusrigidly connected to the axle structures and the apparatus providinginter-axle shear stiffness to enhance the hunting stability of thebogie.

Other advantageous and preferred features of the invention are set forthin the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of exampleonly, with reference to the accompanying drawings in which:

FIG. 1 shows a side view of a bogie retro-fitted with an apparatusaccording to the invention;

FIG. 2 shows a plan view of one side of the bogie;

FIG. 3 shows a detail of a bearing adaptor of the apparatus;

FIG. 4 illustrates a force transmitting device which can be used in theapparatus;

FIG. 5 shows a side view of a bogie manufactured with an apparatusaccording to the invention;

FIG. 6 shows a plan view of the embodiment of FIG. 5;

FIG. 7 illustrates another embodiment of force transmitting device whichcan be used in apparatus according to the invention;

FIG. 8 shows a side view of relevant parts of another embodiment of theinvention;

FIG. 9 shows a plan view of the components seen in FIG. 8;

FIG. 10 shows a side view of a leaf spring used in the embodiment ofFIGS. 8 and 9;

FIG. 11 shows a plan view of the leaf spring of FIG. 10;

FIG. 12 graphically illustrates the performance of the embodiment ofFIGS. 8 and 9;

FIGS. 13 and 14 diagrammatically illustrate the application of theinvention to motorised bogies;

FIG. 15 shows a side view of the motorised bogie of FIG. 14;

FIG. 16 illustrates a stop used in the embodiment of FIGS. 8 and 9;

FIGS. 17 to 21 illustrate different force transmitting devices with adegressive characteristic;

FIG. 22 shows a side view of an embodiment in which provision is madefor axial shear stiffness and a yaw constraint;

FIG. 23 shows a plan view of the embodiment of FIG. 22;

FIG. 24 graphically illustrates the performance of a device such as thatseen in FIG. 17;

FIG. 25 shows a side view of a three-piece bogie and illustrates analternative axlebox suspension arrangement;

FIGS. 26a and 26 b respectively show side and sectional views of anotherdevice which can be used to provide a degressive yaw constraint;

FIGS. 27a and 27 b respectively show side and sectional views of afurther device which can be used to provide a degressive yaw constraint;and

FIGS. 28a and 28 b respectively show side and sectional views of yetanother device which can be used to provide a degressive yaw constraint.

DESCRIPTION OF EMBODIMENTS

FIGS. 1 to 3 illustrate a three-piece self-steering rail bogie 10 towhich an apparatus 12 according to the present invention has beenretro-fitted to provide inter-axle shear stiffness between the axles 16,16.1 of the bogie. As is conventional, wheels 18, 18.1 are fast with theaxles 16, 16.1 of the bogie 10. The axles are supported in respectiveaxle boxes 20, 20.1, located outboard of the wheels, by the usualjournal roller bearings. Side frames 22 are suspended on the axle boxes20, 20.1 and support a transverse bolster 24, on the transverse centreline 26 of the bogie, by means of springs 28.

The apparatus 12 of the invention includes, on each side of the bogie, apair of arms 30, 30.1. The arms are oriented generally in a fore and aftdirection. First ends 32, 32.1 of the arms are connected to therespective axle boxes 20, 20.1 while the opposite, second ends 34, 34.1of the arms lie near to one another on the transverse centre line 26.The arms 30, 30.1 are appropriately shaped lengths of angle sectionsteel with one leg 36 of the angle section vertical and the other leg 38thereof horizontal.

The manner in which the first ends 32, 32.1 of the arms are connected tothe axle boxes 20, 20.1 is now described with particular reference toFIG. 3 of the drawings. The apparatus 12 includes, for each axle box, abearing adaptor 40 which is mounted on the journal bearing 42 of theaxle box and to which the vertical legs 36 of the arms are connected bybolts, welding, riveting, lock-bolting or other suitable means (notshown).

The apparatus 12 also includes, for each bearing adaptor, a shear padassembly 46 which is located between the adaptor and side frame 22,within the pedestal 48 of the side frame. In this embodiment, the shearpad assembly 46 comprises a number of individual, relatively thin rubbershear pads 50. The upper surface of the bearing adaptor 40 is formedwith steps 52, this being allowed by the curvature of the lower surfaceof the bearing adaptor which bears on the journal roller bearing 42 ofthe axle box. Whereas the available space in the pedestal openingbetween the bearing 42 and the pedestal 48 may allow for only a singleshear pad 50 to be placed on the vertical centre line of the bearing inthe retro-fit application under discussion, the steps 52 provide spaceto accommodate stacks of shear pads at positions fore and aft of thecentre line.

The multiple shear pad arrangement allows for appropriate levels ofspring stiffness to be provided between the journal box and pedestaleven in the limited space available in a conventional bogie. Inparticular the arrangement allows longitudinal spring stiffness to bereduced in order to improve the curving, i.e. self-steering, ability ofthe bogie. Although only a single step 52 is shown on each side of theroller bearing centre line in FIG. 3, it should be understood that theremay be several such steps on each side, allowing for the placement ofincreasing numbers of individual shear pads with increasing distancefrom the vertical roller bearing centre line. This in turn can allow forvariations to be made in the level of shear stiffness of the pedestalmounting.

It is however recognised that an inherent problem with a multi-step,multiple shear pad configuration as proposed above is the potentialdifficulty in ensuring that the pads in the various layers and stacksare equally loaded. In an alternative arrangement, shown in FIG. 25,pairs of inclined rubber pads 50 are provided in a configuration whichwill be less susceptible to unequal loading to give the appropriatelevels of longitudinal spring stiffness.

Referring again to FIGS. 1 and 2, although the arms 30, 30.1 are notstrictly radial with respect to the journal bearing 42, it will beunderstood that their orientation is generally radial. For conveniencethe arms are referred to herein as radial arms.

The second ends 34, 34.1 of the arms 30, 30.1 on each side of the bogieare connected to one another by a force transmitting device 60 on thetransverse centre line 26 of the bogie. The device 60 transmits forcesbetween the arms to provide inter-axle shear stiffness for the bogie 10.It will however be understood that transverse forces transmitted betweenthe ends 34, 34.1 of the arms will generate force couples on the journalroller bearings 42, particularly in shock load situations, which couldresult in premature failure thereof. For this reason, the design of thedevice 60 is such that, while it can transmit sufficient force betweenthe arms for the bogie 10 to have adequate inter-axle shear stiffnessfor acceptable hunting stability and curving performance at designspeeds, it does not transmit forces that could generate unacceptablecouples on the journal roller bearings 42.

One example of a suitable device 60 is illustrated in FIG. 4 of thedrawings. The device 60 seen in this Figure has a housing 62accommodating sliding spring cups 64 and 66, a pretensioned compressionspring 68 acting between the cups and a shaft 70 which can slide onbearings 72 through the cups 64 and 66. One end of the shaft carries aneye 74 which, in its application in the present invention, receives theend 34.1 of the arm 30.1. An eye 76 at the other end of the device 60 isfixed to the housing 62 by arms 77 and receives the end 34 of the arm30. The relevant end of the shaft 70 is capable of longitudinal slidingmovement relative to the eye 76.

In situations where the relevant forces transmitted by the radial arms30, 30.1 tend to move the ends 34, 34.1 towards one another, the shaft70 moves to the left in FIG. 4, taking the spring cup 64 with it andthereby applying a further compressive force to the spring 68. Thespring cup 66 abuts a shoulder 78 at the end of the housing and does notmove. At a limit position of movement of the shaft, a nut 80 on theshaft abuts the eye 76. If, on the other hand, the relevant forcestransmitted by the arms 30, 30.1 tend to move the ends 34, 34.1 apartfrom one another, the shaft 70 will move to the right in FIG. 4. The nut80 accordingly pulls the spring cup 66 to the right. The spring cup 64abuts a shoulder 82 of the housing and cannot move so, once again,further compression is applied to the spring 68 in this situation.

The pretension applied to the spring 68 is such that the relativemovement between the ends 34, 34.1 is very small compared to thedeflection which the spring has already undergone in pretensioning itfrom a relaxed state. Thus the maximum force which the spring cantransmit from one radial arm to the other does not substantially exceedthe pretension force in the spring. In practice, the pretension force inthe spring is set in the factory to a value at which it can transmitforces between the arms which are sufficient to give the required levelof inter-axle stiffness for acceptable hunting stability and curvingperformance of the bogie 10, but which are insufficient to generateunacceptable couples on the journal bearings 42.

The force transmitting device 60 described above is only one example ofhow limited force transmission may take place between the arms. Otherembodiments are described below with reference to FIGS. 7 to 12 and 17to 21.

Specific reference has been made to the apparatus 12 being of aretro-fit design. The ability to retrofit an apparatus of this nature isof course advantageous. It will however be understood that in the caseof new bogies, corresponding apparatus can be installed at the time ofmanufacture. In this case, the radial arms 30, 30.1 can be manufacturedintegrally as the wings of wing-type axle boxes. An example of such aconstruction is illustrated in FIGS. 5 and 6 which show radial arms 30,30.1 formed integrally with wing-type axle boxes 20, 20.1.

The wing-type axle boxes of the new bogie depicted in FIGS. 5 and 6 makeuse of two springs 84 per axle box, located respectively fore and aft ofthe vertical centre line, to achieve appropriate levels of longitudinalspring stiffness. However, bogies of original manufacture could alsomake use of a bearing adaptor and shear pad assembly located within theopening of the pedestal frame as described above for the retro-fitapplication. In these cases the radial arm could either be bolted on ormade integral with the adaptor. Alternatively it would be possible in anew bogie to increase the size of the pedestal opening to accommodate alarger, single shear pad on the vertical centre line instead of anassembly of shear pads 50 as described above for the assembly 46. With alarger and softer single shear pad it would also be possible to achievea softer longitudinal spring effect in order to improve the curvingcharacteristics of the bogie.

A major advantage of the invention as exemplified above is that, whileadequate inter-axle shear stiffness is provided, the arms 30, 30.1 canbe of relatively lightweight construction, thereby adding relativelylittle to the unsprung mass of the bogie 10 compared to conventionaldesigns. Although specific mention has been made of radial arms 30, 30.1which are of angle section, it will be understood that channels,I-sections or other cross-sections could also be used.

It will be understood that the force transmitting device 60 of FIG. 4has a very high level of initial stiffness to transmit lateral loadsbetween the radial arms. After the initial spring pretension has beenovercome there is little or no increase in the lateral loads which thedevice 60 can transmit between the radial arm, it being understood thatthe spring characteristic and the pretension applied thereto are setsuch that the lateral load which is transmitted after the pretension hasbeen overcome is insufficient to cause damage to the journal bearings.While a high level of initial stiffness is appropriate to transmit thelateral load, it is however believed that a few millimeters ofdeflection should be allowed to take place.

FIG. 7 illustrates another force transmitting device 90, similar to thedevice 60, which allows for several millimeters of deflection prior tothe pretension force in the coil spring 68 being overcome. In this case,the device 90 includes pairs of opposed Belleville or spring washers 92at either end. The spring characteristic of the Belleville springcombinations is such they can accommodate a few millimeters of initialdeflection in either direction.

FIG. 7 shows the pairs of Belleville washers with their concavitiesdirected away from one another at one end and towards one another at theother end, but it will be understood that the arrangement could be thesame at both ends.

As an alternative to Belleville washers, ring-shaped springs having anannular core of rubber or suitable polymer material, such as Vescoflex™,moulded between annular steel plates could be used.

FIGS. 8 and 9 illustrate another embodiment of the invention which usesa different type of force transmitting device in a radial armconfiguration. This embodiment uses a pair of pretensioned leaf springs100 as the force transmitting device. A typical one of these leafsprings is illustrated, in its manufactured state, in FIGS. 10 and 11.The spring 100 has straight ends 102 and 104 with a curved middleportion 106. The straight ends 102 of the springs 100 are clamped bybolts 108 extending through holes 110 to the radial arm 30.1 with thesprings parallel to one another. The radial arm 30.1 in this case has abox section which accommodates the springs spaced apart laterally fromone another.

A pulling device (not shown) is then inserted through holes 112 at theopposite ends of the springs. Tension is applied to the pulling deviceto pull the springs into a straight condition or even past straight. Astop 114 is fitted to each spring at a point 116 corresponding to theend of the portion 106 which was curved prior to the pretensioningoperation just described.

An example of a suitable stop 114 is shown in FIG. 16 of the drawings.This stop 114 includes an upright plate 118 attached at its upper andlower ends to internally threaded members 120. Spaced apart from theplate 118 is a pair of lugs 122 also attached to the members 120. Theleaf spring 100 can slide in the gap defined on one side by the plate118 and on the other side by the lugs 122.

A set-screw 124 extending through a tapped hole in the plate 118 is usedto anchor the stop to the leaf spring at the chosen position 116. Thusit will be understood that the stop is in fact slipped along the leafsprings 100 to the position 116 where they are anchored by means of theset-screws 124.

Set screws 126 extend through the members 120 as illustrated. Once thestops 114 have been fixed to the leaf springs at the correct positions,the projecting ends 128 of the set screws 126 bear against the uprightwalls of the box section radial arm 30.1. By adjusting the set screws126 it is possible to bring the leaf springs into orientations in whichthey are straight and parallel to one another. The set screws are inturn locked in position by grub screws 130. The inner end of the otherradial arm 30 carries a transverse member 132, termed a “crosshead”,which is positioned on the transverse centre line 26 of the bogie andwhich locates slidably between the free ends of the leaf springs 100projecting from the other radial arm. In situations where shear forcesbetween the axles tend to move the adjacent ends of the arms 30, 30.1towards or away from one another, the crosshead 132 will apply a forceto one or other of the leaf springs in a manner tending to lift its stop114 off the radial arm 30.1.

Because of the pretension force stored in each leaf spring and thebearing of the stops 114 against the radial arm 30.1, the free ends ofthe leaf springs act in the manner of pretensioned cantilevers having alength defined between the position 116 and the crosshead 132. Thuslateral force can be transmitted between the radial arms with littleinitial lateral deflection as initial loading up to the value of thepretension force takes place.

However, if the lateral force is sufficient to overcome the prestress inthe relevant leaf spring, the set screws 126 of the stop 114 on thatleaf spring will be lifted off the radial arm 30.1. Thereafter the fulllength of leaf spring acts in cantilever mode to take the appliedlateral force. Clearly the shorter cantilever which acts initially issubstantially stiffer than the longer cantilever which acts after thestop has been lifted. Accordingly the spring can flex more readily overits full length to take further applied loading without substantialtransmission of the force between the radial arms 30, 30.1 after thestop has lifted.

This is illustrated in FIG. 12 which shows a theoretical plot ofdeflection on the horizontal axis against transmitted force on thevertical axis. In the initial stage A where the applied load isinsufficient to overcome the prestress in the spring it will be seenthat the spring can transmit a substantial load with very littledeflection. In practice, as mentioned previously in connection with thedevice 60 of the first embodiment, it is desirable for there to be a fewmillimeters only of deflection during this stage.

The point B in the graph represents the point at which the applied loadis equal to the prestress in the spring and the stop lifts off theradial arm. Thereafter in stage C the load which the spring can transmitincreases only very slightly with increasing deflection.

As in the previous embodiments, the design is such that adequate lateralforce can be transmitted during stage A to provide a suitable level ofinter-axle shear stiffness. Thereafter the maximum transmitted force isinsufficient to cause damage to the journal roller bearings.

Referring again to FIG. 7, the Belleville springs 92 provide the fewmillimeters deflection represented by stage A in FIG. 12.

An important advantage which the embodiment of FIGS. 8 and 9 has overthat of FIGS. 4 and 7 is the fact that the leaf spring device is morecompact in a lateral sense than the transverse coil spring device. Theleaf spring device may accordingly be preferred in situations wherethere are obstacles close to the rail track which could interfere with abogie fitted with a transversely extending device such as the devices60.

Another advantage of the leaf spring device of FIGS. 8 and 9 is that theinitial force required to lift the stop 114 off the radial arm 30.1 canbe varied merely by varying the length of the lever arm defined betweenthe position 116 and the crosshead 132, i.e. by varying the position ofthe stop on the leaf spring.

It will accordingly be understood that the use of leaf springs asdescribed above lends itself to a particularly compact and versatiledesign able to provide both inter-axle shear stiffness and, as describedbelow, a longitudinal yaw constraint.

The embodiments described above are applied to three-piece self-steeringbogies. However the invention has wider application. FIG. 13 illustratesthe application of the invention to a motorised, self-steering bogiehaving axles 200 fitted with motors 202. In this case, shear stiffnessis provided by a transverse force transmitting device 204, correspondingto the device 60 used in the previous embodiments and acting on thetransverse centre line of the bogie between fore-and-aft extendingradial arms 206 and 208 corresponding to the arms 30, 30.1.

FIG. 14 illustrates the application of the invention to a motorisedbogie having axles 300 fitted with motors 302. Shear stiffness in thiscase is provided by a leaf spring device 304 as described above inrelation to FIGS. 8 and 9, the leaf springs being attached to an arm 306extending rearwardly from one of the motor/axle assemblies and actingagainst a crosshead 308 carried on the transverse centre line of thebogie by an arm 310 extending forwardly from the other motor/axleassembly.

From FIG. 15, which shows a side view of the motorised bogie of FIG. 14,it will be seen that the arms 306, 310 are radially orientated andcorrrespond to the arms 30,30.1.

It will also be noted that in FIGS. 13 and 14 the force transmittingdevice is located inboard of the bogie wheels whereas in the previousembodiments, the devices are arranged outboard. Those skilled in the artwill appreciate that inboard location is possible because of theinter-axle space which is available with motorised bogies.

Other embodiments of force transmitting device, with a degressivecharacteristic, are illustrated in FIGS. 17 to 21. Referring to FIG. 17,there is an annular cam member 418 composed of mating cam segments 418.1and 418.2 and a series of circumferentially spaced balls 454 which seat,in the dead centre position, in a recess 422 formed by the mating camsegments. A biasing force to hold the balls 454 in this position isprovided by a spring 456 acting on a cone 458. The spring 456 surroundsa shaft 460 and is pretensioned by a sleeve 462 which acts against ashoulder 464 of the cone and screws onto the shaft at a thread 466. Theballs 454 are retained between the end surface 468 of the sleeve and apiston 470 which is locked to the shaft by a lock nut 472 and whichbears against the end face of the cone 458.

The dimensions are such that the ball-retaining gap between the opposingfaces of the sleeve 462 and piston 470 is slightly greater than the balldiameter. Thus the balls are not tightly gripped between these faces andare able to move radially in the gap, as described below.

The cam segments 418.1, 418.2 are pressed into a cylinder 474 and areheld between an internal shoulder 476 of the cylinder and an internalguide nut 478. Bushes 480 and 482 are provided in the cylinder 474 andin the sleeve 462 to allow for longitudinal sliding movement of thepiston in the cylinder and of the sleeve in the guide nut respectively.

The shaft and cylinder carry respective couplings 484 and 486 by meansof which they can be connected to members between which forces are to betransmitted, in the present case the inner ends 34, 34.1 of the railarms 30, 30.1.

In the rest or dead centre position seen in FIG. 17 the balls 454 areretained in the recess 422 by the large diameter end of the conicalsurface of the cone 458. When relative movement takes place between theends 34, 34.1 either towards or away from one another, the shaft 460 andcylinder 474 move relative to one another. Depending on the direction ofrelative movement, either the sleeve or the piston pushes on the balls.With application of a large enough force, the force of the spring 456 isovercome and the cone 458 slides on the shaft 460 to compress the springfurther. The balls move out of the recess 422 and over the profiled camsurfaces 424. Since the balls are acted upon by progressively smallerdiameters of the conical surface of the cone, there is a progressivelydiminishing, i.e. degressive, restoring force.

FIGS. 18 and 19 show modified versions of the FIG. 17 embodiment.Components corresponding to those in FIG. 17 are designated by likenumerals. In FIG. 18, conical disc springs, i.e. Belleville springs 488,apply the necessary bias to the balls 454 in place of the cone andspring configuration of FIG. 17. In FIG. 19 rubber springs 490 are usedin place of the disc springs 488. Despite the different springarrangements employed in FIGS. 18 and 19 it will be appreciated thatthese embodiments operate in a fashion similar to FIG. 17, with the discor rubber springs initially applying a large restraint to unseating ofthe balls from the recess 422 and thereafter the restoring forcediminishes, i.e. degresses, with increasing deflection.

FIGS. 20 and 21 show another embodiment of force transmitting devicewhich is an approximate reversal of the configuration in FIG. 17. Here,coil springs 492 in spring housings 494 on the cylinder 474 act inwardlyon individual balls 454 to retain them in recesses 422 in the shaft 460which can slide in the cylinder in bushes 496. As illustrated, there isa number of balls and corresponding springs which are circumferentiallyand longitudinally spaced apart from one another. In an alternativeconfiguration there could be a plurality of balls spaced apart angularlyin the same circumferential plane, i.e. without longitudinal spacing.This would decrease the overall length of the device.

It will be understood that the devices described above with reference toFIGS. 17 to 21 can be used as the force transmitting device in theearlier embodiments of FIGS. 1 and 2, FIGS. 5 and 6 or FIG. 13. As isthe case with the previously described devices for this purpose, thecharacteristics of the force-transmitting devices of FIGS. 17 to 21 aresuch that a limited force can be transmitted between the radial arms 30and 30.1 which is sufficient to achieve the required level of inter-axlestiffness but insufficient to place unacceptable couples on the journalroller bearings of the wheelsets, particularly in shock load conditions.

In addition to providing for transmission of a limited lateral forcebetween the ends of the radial arms 30, 30.1, the devices of FIGS. 17 to21 can also be used to provide degressive yaw constraints for thewheelsets of a rail bogie to ensure that on straight track there is arelatively high resistance to yawing of the wheelsets while on curvedtrack, where yawing movements must be accommodated if the wheelsets areto attain radial orientations for proper self-steering to take place, areduced resistance to yawing is required.

The degressive force transmitting devices of FIGS. 17 to 21 could, forinstance, be arranged to act between the axle boxes of wheelsets on thesame side of the bogie i.e. in the manner described with reference toFIG. 7 in the specification of South African patent 94/1641, to whichreference should be made for the details. Alternatively such devicescould be arranged to act between the bogie frame and the axleboxes ofthe wheelsets.

FIGS. 22 and 23 illustrate how degressive force transmitting devicessuch as those seen in FIGS. 17 to 21 can be used both to constrainwheelset yawing in a degressive manner and to provide inter-axlestiffness according to this invention. As before these Figures show athree piece, self steering bogie 10 with wheelsets 18, 18.1 journalledin axle boxes 20, 20.1 on which side frames 22 are suspended. Radialarms 30, 30.1 are connected to the axle boxes on each side of the bogieand extend towards one another with a force transmitting device 60acting on the transverse centre line of the bogie between the adjacentends 34, 34.1 of the radial arms. The device 60 may be any one of thedegressive force transmitting devices described above with reference toFIGS. 17 to 21. The characteristics of the device, determined inter aliaby the spring pretension force and the profile of the cam member againstwhich the balls act, is set such that the maximum force which can betransmitted between the radial arms is sufficient to provide adequateinter-axle shear stiffness for hunting stability at high bogie speedsbut insufficient to place unacceptable couples on the wheelset journalbearings.

This is illustrated by FIG. 24 which shows a graph similar to that ofFIG. 12. As shown here a large force can initially be transmitted withlittle deflection, i.e. movement of the ends 34, 34.1 of the radial arms30, 30.1 towards or away from one another. Thereafter there is little orno increase in transmitted load with further deflection.

It will of course be understood that in each embodiment described above,the design of the force transmitting device is such that, irrespectiveof the amount of lateral movement between the adjacent ends of theradial arms, it is unable to transmit lateral forces which exceed apredetermined maximum force. The selected maximum force is great enoughto generate a level of inter-axle shear stiffness consistent withacceptable hunting stability of the bogie but is insufficient togenerate force couples on the axle box journal bearings which exceedwhat is considered to be an acceptable limit.

Referring again to FIGS. 22 and 23 another force transmitting device60.1, similar to the device 60 and having a degressive characteristic asdescribed above is used in the yaw constraint mode. It is seen actingbetween the radial arms 30, 30.1 with the cylinder of the device mountedto a bracket 112 on the radial arm 30 and the shaft 113 of the deviceconnected to a bracket 114 on the other radial arm 30.1. The device 60.1accordingly applies a double-acting degressive yaw constraint betweenthe linked axleboxes.

FIGS. 26a and 26B, FIGS. 27a and 27 b and FIGS. 28a and 28 b illustratethree further embodiments of devices which can be used to provide adegressive yaw constraint feature in a self-steering bogie.

Referring firstly to FIGS. 26a and 26 b, there is shown an embodiment510 which includes a back plate 512 carrying spaced apart, projectingsupport pins 514 between which a leaf spring 516 is engaged. A cammember 518 is connected centrally to the leaf spring by studs 520. Thecam member has a central recess 522 and profiled cam surfaces 524arranged symmetrically on either side of the central recess.

The device 510 also includes a roller 526 carried rotatably by a lever528 consisting of spaced apart arms 530 between which the roller islocated. Between the roller and its lower end, the lever 528 issupported pivotally on a pin 532 projecting from the back plate 512. Atthe lower end of the lever a transverse pin 534 is attached via aspherical bearing 536 to the end of a link 538.

The device 510 serves to transmit forces between the link 538 and theback plate 512. In a practical application which the device is used toprovide a longitudinal yaw constraint, the back plate may be fixed to orbe part of the bogie frame with the link 538 being an axle box linkextending from an axle box. The device 510 then serves to transmitlongitudinal forces between the axle box and the bogie frame to providea degressive yaw constraint for the relevant axle to improve huntingstability.

FIG. 26a shows the device at a central or dead centre position with theroller 526 seated in the recess 522. The roller is held in this positionby the action of the leaf spring 516, which is pretensioned to provide apredetermined biasing force. Movement of the axle box link, for instancein the direction indicated by the arrow 40, in response to yawingmovement of the associated axle relative to the bogie frame, causes thelever 528 to rotate about the axis of the pin 532. There is initiallyconsiderable resistance to this movement as a result of the seating ofthe roller in the recess 522. However if the force applied by the link538 is sufficient to unseat the roller from the recess, there will be aprogressively decreasing restoring force, i.e. a degressive resistance,as the roller moves over the relevant cam surface as indicated by thearrow 542. The device 510 accordingly transmits the force from the linkto the back plate, i.e. from the axle box to the bogie frame, in adegressive manner with the magnitude of the transmitted force decreasingwith increasing movement of the link.

It will be understood that if the link 538 moves in the oppositedirection with sufficient force to unseat the roller from the recess,there will be a similar degressive restraint as the roller moves overthe other cam surface 524 in the direction of the arrow 544. Thus it canbe seen that the device 510 is double-acting in the sense that thedegressive restraint is applied irrespective of the direction ofrelative movement between the axle box link 538 and the back plate.

Components in FIGS. 27a and 27 b which correspond to those in FIGS. 26aand 26 b are designated by the same reference numerals. In this case thecam member 518 is clamped between two spring blades 546 supported by theback plate 512. There is once again a roller 526 carried by a lever 528.

In the practical example mentioned above, forces are again transmittedbetween an axle box to which the link 538 is connected and a bogie framein a degressive manner, with an initially large resistance to unseatingof the roller 526 and thereafter a progressively diminishing restoringforce as the roller moves further and further along one or other of thecam surfaces 524 with increasing movement of the link 538, i.e. withincreased yawing movement of the axle.

In FIGS. 28a and 28 b, like components are again designated with likereference numerals. In this case, the leaf or blade springs of theembodiments of FIGS. 26 and 27 are replaced by a pretensioned coilspring 548 which acts between the pivot pin 532 and a lug 550 on the cammbmer 518 which is pivoted to the back plate 512 at a pivot 552.

In FIGS. 26 to 28 the spring force will in each case be kept as low aspractically possible to reduce wear on the roller 526 while neverthelesscatering for the transmission of appropriate yaw constraining forces inthe required, degressive manner.

In the context of a longitudinal yaw constraint and referring again tothe embodiment seen in FIGS. 8 and 9 an added advantage is the abilityto accommodate a longitudinal yaw constraint device between the leafsprings. The yaw constraint could, for instance, be similar to thatillustrated in FIGS. 22 and 23. In the proposed arrangement one end ofthe degressive yaw constraint would be attached to a vertical pin 140forming part of the crosshead 132 and the opposite end to another pin142 extending vertically through the radial arm 30.1 between the springs100. It will be appreciated that in this way both inter-axle shearstiffness and a longitudinal yaw constraint can be provided verycompactly.

I claim:
 1. An inter-axle shear stiffening apparatus for a self-steeringrail bogie having axle structures including axles which are journalledin axle box bearings, the apparatus comprising arms which are rigidlyconnected or connectable to respective axle structures of the bogie toextend towards one another from the axle structures in generally foreand aft directions, and lateral force transmitting means for actingbetween the arms to transmit lateral forces between them whileaccommodating relative lateral movement between the arms, wherein,irrespective of the extent of relative movement between the arms, thelateral force transmitting means is only capable of transmitting betweenthem lateral forces of limited, predetermined magnitude which providethe bogie with inter-axle shear stiffness to enhance hunting stabilityof the bogie but are insufficient to impose excessive force couples onthe axle box bearings.
 2. An apparatus according to claim 1 wherein thelateral force transmitting means is arranged to transmit lateral forcesbetween adjacent ends of the arms substantially on a transverse centreline of the bogie between the axles.
 3. An apparatus according to claim2 wherein the lateral force transmitting means is arranged to transmitlateral forces between the arms substantially in the plane of the axlebox bearings.
 4. An apparatus according to claim 1 wherein the arms arearranged to be substantially radially oriented with respect to theaxles.
 5. An apparatus according to claim 1 wherein the lateral forcetransmitting means is arranged initially to transmit between the armsrelatively large lateral forces, up to the predetermined magnitude, forrelatively small relative movement between the arms and thereafter totransmit little or no further forces between the arms for relativelylarge relative movement between the arms.
 6. An apparatus according toany one of the preceding claims wherein the lateral force transmittingmeans includes a spring to resist relative lateral movement between thearms, the spring being pretensioned to a value not substantially lessthan the predetermined magnitude.
 7. An apparatus according to claim 6wherein the spring is a coil spring.
 8. An apparatus according to claim6 wherein the spring comprises one or more leaf springs.
 9. An apparatusaccording to any one of claims 1 to 5 wherein the lateral forcetransmitting means comprises a cam member presenting a cam surface inwhich a recess is formed, a detent and spring means biasing the detentto seat it in the recess, the detent when seated in the recess resistingrelative movement between the arms while lateral forces are transmittedbetween them, with the arrangement being such that on transmission oflateral forces between the arms of the predetermined magnitude thedetent is unseated from the recess and moves over the cam surface withlittle further transmission of lateral force between the arms.
 10. Aself-steering rail bogie, comprising: at least two axle structuresincluding axles journalled in axle box bearings; and an inter-axle shearstiffening apparatus, said inter-axle shear stiffening apparatuscomprising: an arm rigidly connected or connectable to each of said atleast two axle structures of the bogie, said arms extending toward oneanother from said axle structures; a lateral force transmittingconnector connected between and acting between the arms to transmitlateral forces between said arms such that, irrespective of the extentof relative movement between said arms, the lateral force transmittingconnector transmits lateral forces of limited predetermined magnitude,said transmitted lateral forces being sufficient to provide inter-axleshear stiffness to enhance the hunting stability of the bogie butinsufficient to impose excessive force couples on the axle box bearings.11. A self-steering rail bogie according to claim 10 wherein the bogieis a three piece bogie.
 12. A self-steering rail bogie according toclaim 11 which comprises an inter-axle shear stiffening apparatuslocated outboard of wheels carried by the axles on each side of thebogie.
 13. A self-steering rail bogie according to claim 10 wherein thebogie is a motorised bogie.
 14. A self-steering motorized rail bogie,comprising: at least two axle structures including axles journalled inaxle box bearings, wherein said axles carry wheels; and an inter-axleshear stiffening apparatus, wherein the inter-axle shear stiffeningapparatus is located inboard of said wheels, said inter-axle shearstiffening apparatus comprising: an arm rigidly connected or connectableto each of said at least two axle structures of the bogie, said armsextending toward one another from said axle structures; a lateral forcetransmitting connector connected between and acting between the arms totransmit lateral forces between said arms such that, irrespective of theextent of relative movement between said arms, the lateral forcetransmitting connector transmits lateral forces of limited predeterminedmagnitude, said transmitted lateral forces being sufficient to provideinter-axle shear stiffness to enhance the hunting stability of the bogiebut insufficient to impose excessive force couples on the axle boxbearings.
 15. A self-steering rail bogie according to any one of claims10 to 14 and comprising degressive yaw constraint means acting betweenthe axles to constrain yawing movements between the axles.
 16. Aninter-axle shear stiffening apparatus for a self-steering bogie havingfirst and second axle structures including axles that are journalled inaxle box bearings, comprising: a first arm rigidly connected orconnectable to the first axle; a second arm rigidly connected orconnectable to the second axle, said first and second arms extendingtoward each other when connected to the first and second axles,respectively; a lateral force transmitting connector connected betweensaid first and second arms, said lateral force transmitting connectorincluding a stiffening mechanism that transmits between said armslateral forces having magnitudes less than a predetermined value forrelatively small relative movement between the arms and transmitsbetween said arms little or no lateral forces having magnitudes greaterthan said predetermined value, even for relatively large relativemovement between said arms.
 17. An inter-axle shear stiffening apparatusfor a self-steering bogie having first and second axle structuresincluding axles that are journalled in axle box bearings, comprising: afirst arm rigidly connected or connectable to the first axle; a secondarm rigidly connected or connectable to the second axle, said first andsecond arms extending toward each other when connected to the first andsecond axles, respectively; a lateral force transmitting connectorconnected between said first and second arms, said lateral forcetransmitting connector including a stiffening mechanism that transmitsbetween said arms lateral forces having magnitudes less than apredetermined value for relatively small relative movement between thearms and transmits between said arms little or no lateral forces havingmagnitudes greater than said predetermined value, even for relativelylarge relative movement between said arms, wherein said lateral forcetransmitting connector comprises a spring, said spring beingpretensioned with a force that is not substantially less than saidpredetermined value.
 18. An inter-axle shear stiffening apparatus for aself-steering bogie having first and second axle structures includingaxles that are journalled in axle box bearings, comprising: a first armrigidly connected or connectable to the first axle; a second arm rigidlyconnected or connectable to the second axle, said first and second armsextending toward each other when connected to the first and secondaxles, respectively; a lateral force transmitting connector connectedbetween said first and second arms, said lateral force transmittingconnector including a stiffening mechanism that transmits between saidarms lateral forces having magnitudes less than a predetermined valuefor relatively small relative movement between the arms and transmitsbetween said arms little or no lateral forces having magnitudes greaterthan said predetermined value, even for relatively large relativemovement between said arms, wherein said lateral force transmittingconnector comprises: a cam having a cam surface that includes a recesstherein; a detent seated in said recess; and a spring urging said detentand said cam together such that said detent resists relative movementand transmits lateral forces between said arms when seated in saidrecess as long as the lateral forces are less than said predeterminedvalue and unseats from said recess and transmits substantially nofurther lateral forces when the lateral forces exceed said predeterminedvalue.